A Pulse-Driven LC-VCO with a Figure-of-Merit of -192dBc/Hz Aravind Tharayil Narayanan, Kento Kimura, Wei Deng, Kenichi Okada, and Akira Matsuzawa Tokyo Institute of Technology, Japan b. b. Matsuzawa Matsuzawa & Okada Lab. & Okada Lab. y y
Contents u Motivation u Tackling Efficiency: Class-C VCO u Efficiency and MOS Sizing u Effects of Large MOS u AM-PM Conversion Phenomenon u Pulse Drive Technique u Proposed VCO u Simulation and Measurement Results u Conclusion 1
Motivation Low power TRx is required for next gen portable devices 19mA VCO 38% RX 62% 30mA [1] H. Darabi, JSSC 2011. VCO – A major power consumer in TRx. VCO for next generation wireless devices u High purity u High efficiency u Small area 2
Tackling Efficiency: Class-C VCO VDD V DS V DD V P V N V gbias 2 Class-B ≈ I B π I DS V TH M1 M2 ≈ I B −Φ Φ Class-C I DS - ϖ - ϖ 0 ϖ ϖ I B C Tail 2 2 Ø High current efficiency [2] A. Mazzanti and P. Andreani, JSSC 2008. 3
Efficiency and MOS sizing V DS V DD V TH ! !"# = ! !! − ( ! !" − ! !" ) ! V GS I max1 For high efficiency Φ 1 −Φ 1 I DS1 Ø Large A max Small MOS I max2 Ø Small V GS Ø Small conduction angle −Φ 2 −Φ 2 I DS2 - ϖ - ϖ 0 ϖ ϖ 2 Large MOS 2 Ø Large MOS required for better efficiency [2] A. Mazzanti and P. Andreani, JSSC 2008. 4
Effects of Large MOS VDD Behavior of C gs C GS V P V N C H C gs C T V gbias C L V TH V DS+TH V GS M1 M2 C gs,M1 C gs,M2 (saturation) V Tail C Tail (cut-off) Ø Tank capacitance is susceptive to V GS variations. 5
AM-PM Conversion in Class-C VCO VDD Time Domain Analysis V V P V N V DS V DD C GS V TH V GS ∆ V GS1 ∆ V GS2 -R t C GS Bias ∆ C 1 ∆ C 2 C GS C H t C T f f 0 - Δ f 1 f 0 - Δ f 2 C L δ f -2 ϖ - ϖ 0 ϖ 2 ϖ V GS Ø Variations in C GS translates to phase noise. 6
AM-PM conversion- Contd. -90 simula � on Large AM-PM Phase Noise [dBc/Hz] with AM-PM -95 without AM-PM -100 -105 Small Φ -110 -115 -0.3 0.0 0.3 0.6 V gbias [V] Ø Smaller Φ with smaller transistor size. 7
Issue of Class-C VCO V V DS I DS V DD V TH V gbias V GS t t - ϖ - ϖ - ϖ - ϖ 0 0 ϖ ϖ ϖ ϖ 2 2 2 2 V GS -V TH must be small for small Φ Large MOS is required for larger current Ø Smaller Φ with smaller transistor size. 8
Proposed Pulse-Driven VCO V V DS I DS V DD V TH V gbias V GS t t - ϖ - ϖ 0 ϖ ϖ V 2 2 V DS I DS V DD V TH V GS V SS t t - ϖ - ϖ - ϖ - ϖ 0 0 ϖ ϖ ϖ ϖ 2 2 2 2 Conduction angle is independent of MOS size. 9
Analysis: AM-PM Conversion VDD Time Domain Analysis V V P V N ∆ V GS1 ∆ V GS2 V DS V DD V TH C GS V GS 0 t -R C GS C T Pulse Drive C L C GS t C H C T f f 0 - Δ f f 0 - Δ f f 0 C L t -2 ϖ - ϖ 0 ϖ 2 ϖ V GS AM-PM translation is minimized. 10
Proposed Circuit Schematic conduction angle VDD control VDD VDD Amplitude V P V N regenerator IB IB R b R b C b C b V bp V bn M1 M2 V Tail M Tail C Tail 11
Pulse Drive: Startup A Tank V DD Cond. Angle Amplitude Control Regeneration V(N B ) ϖ VDD θ N B V Init V bp IB V TH R b C b M b V p Sense Class-AB Class-B Induced Class-C V bp V DD High robustness 0 ϖ t 12 θ
Pulse Drive: Startup Contd . A Tank V DD Cond. Angle Amplitude Control Regeneration V(N B ) ϖ VDD θ N B V Init V bp IB V TH R b C b M b V p Sense Class-AB Class-B Induced Class-C V bp V DD 0 ϖ t 13 θ
Pulse Drive: Steady State A Tank V DD Cond. Angle Amplitude Control Regeneration V(N B ) ϖ θ VDD N B V Init V bp IB V TH R b C b M b V p Sense Class-AB Class-B Induced Class-C V bp V DD High Efficiency 0 ϖ t 14 θ
Noise from the additional MOS V DS V DD L P C P C CC 0 V P T 1 ISF L P C P τ V N Pulse Generator 0 I DS τ V DD -2 ϖ - ϖ 0 2 ϖ ϖ Delay introduced by the inverter is within safe ISF region. Delay becomes trivial in advanced processes. 15
Noise Contribution V P V N Tank 40 P_Drive P_Drive Noise Contribution (%) N 1 N 2 30 M CC M CC 20 M Tail C Tail V Tail 10 M BIAS VDD IB 0 N 1 R BIAS Misc. M CC M TAIL R BIAS M BIAS Tank C b M b Components V p Noise introduced by the driver circuitry is small. 16
Chip Micrograph Reference VCO Proposed VDD VDD V P V N V P V N V gbias Pulse Pulse Drive Drive M1 M1 M2 M2 V Tail V Tail C Tail C Tail 250 250 62 45 Pulse Drive 500 500 17
Measurement Results -50 Phase Noise [dBc/Hz] -60 -70 Reference VCO -80 P dc = 2.54mW -90 FoM = -190dBc/Hz -100 -110 This work -120 P dc = 2.05mW -130 FoM = -192dBc/Hz -140 -150 1k 10k 100k 1M 10M Offset Frequency [Hz] 18
Performance Comparison CMOS Frequency Phase Noise Pdc FoM Process [GHz] [dBc/Hz] [mW] [dBc/Hz] [1] JSSC2008 130nm 4.9 -130@1MHz 1.30 -196 [2] VLSI2009 180nm 4.5 -109@1MHz 0.16 -190 [3] JSSC2013 180nm 4.84 -125@1MHz 3.40 -193 [4] ESSCIRC2011 90nm 5.1 -120@1MHz 0.86 -192 [5] JSSC2013 65nm 3.7 -142@3MHz 15.0 -192 [6] JSSC2013 65nm 4.8 -144@10Mhz 4.00 -191 This Work 180nm 3.6 -124@1MHz 2.05 -192 [1] A. Mazzanti and P. Andreani, JSSC 2008. [2] K. Okada et al ., VLSI 2009. [3] W. Deng et al ., JSSC 2013. [4] M. Tohidian et al ., ESSCIRC 2011. [5] M. Babaie et al ., JSSC 2013. [6] L. Fanori et al ., JSSC 2008 19
Conclusion Ø A phenomenon in class-C VCO due to which AM noise is up-converted to PN is identified. Ø A new technique namely “pulse-drive” is proposed to alleviate AM-PM conversion issue. Ø The proposed pulse-drive technique avoids AM-PM conversion without sacrificing efficiency. Ø A VCO is implemented using the proposed pulse- drive technique and tested to verify the claims. Ø The proposed circuit is however process dependent and has limited frequency of operation. 20
Simulated Waveforms (1) 0.9 6.E-03 0.8 5.E-03 0.7 4.E-03 0.6 Current (A) Voltage (V) 3.E-03 0.5 0.4 2.E-03 0.3 1.E-03 0.2 0.E+00 0.1 0 -1.E-03 3.85E-07 3.85E-07 3.85E-07 3.85E-07 3.85E-07 Time (s) 21
Simulated Waveforms (2) 22
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